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### Question

A train passes two persons walking in the same direction as the train. The time it takes to move past the man running at 4km/h is 6sec, whereas the time it takes to cross the other man running at 11km/h is 7sec. What is the speed of the train?

**A**

53 km/h.

**B**

54 km/h.

**C**

52 km/h.

**D**

55 km/h.

**Soln.**

**Ans: a**

Let the speed of the train be v km/h. Length of the train calculated with the data for the first man = $(v - 4) × 6$. It should equal the length obtained from the data for the second man. So $(v - 4) × 6$ = $(v - 11) × 7$. Please note that we have not converted seconds to hours because that factor will ultimately cancel away. Solving for v we get 53km/h.